Laser spot tracking with off-axis angle detection

Abstract

A laser spot tracker comprising a quadrant detector. A portion of a spot of laser light reflected from an object being illuminated (OBI) may be defocused to occupy a significant portion such as one-third of the field of view, while another portion remains focused, therefore allowing for quick calculation of the spot centroid. With such a “composite spot”, multiple target (OBI) positions may simultaneously be defined in elevation and azimuth with respect to null by analyzing the energy in each quadrant. The X and Y angle information (off null) for multiple targets (OBIs), and their codes may be displayed. For a large, defocused spot, two segmented multi-element detectors may be used, one in front of and the other behind the focal plane to reduce the effects of hot spots in a spot of laser light collected from an object being illuminated.

What is claimed is: 
     
       1. Method of locating at least one object being illuminated by a laser designator comprising:
 providing a tracker having a quadrant detector in a field of view; 
 receiving laser light scattered by the at least one object being illuminated; 
 causing the received laser light to impinge as a corresponding at least one spot on the quadrant detector; 
 for each of the spots of received laser light impinging on the detector, determining an angle of the spot of the received laser light relative to a center of the field of view; and 
 increasing a spot size for a defocused portion of the received laser light, a remaining focused portion of the received laser light impinging as a relatively small spot on the detector. 
 
     
     
       2. The method of  claim 1 , further comprising:
 increasing a size of selected ones of the multiple spots at the detector so that a given spot covers approximately one-third of the field of view. 
 
     
     
       3. The method of  claim 2 , further comprising:
 using the increased-in-size spots to derive off null positions of objects being illuminated. 
 
     
     
       4. The method of  claim 1 , further comprising:
 simultaneously processing multiple targets having been illuminated with different PRF codes. 
 
     
     
       5. The method of  claim 1 , further comprising
 displaying an angle with respect to null for each of the spots of received laser light. 
 
     
     
       6. The method of  claim 1 , wherein sizes of the spots are increased to be sufficiently large to impinge on multiple quadrants of the detector, and further comprising:
 determining centroids for the spots: and 
 providing outputs representing elevation and azimuth of the centroids of the spots relative to a boresight direction. 
 
     
     
       7. The method of  claim 6 , further comprising:
 providing the outputs representing elevation and azimuth for each of multiple objects being illuminated, each tagged with a code to allow for identification of their respective designators. 
 
     
     
       8. The method of  claim 1 , further comprising:
 calculating azimuth and elevation angular co-ordinates for centroids of the spots by measuring energy of the received laser light in each quadrant of the detector. 
 
     
     
       9. The method of  claim 1 , further comprising:
 increasing a size of the at least one spots at the detector so that a given spot covers approximately one-third of the field of view. 
 
     
     
       10. The method of  claim 9 , further comprising:
 using the increased-in-size spots to derive off null positions of objects being illuminated. 
 
     
     
       11. The method of  claim 1 , further comprising:
 simultaneously processing multiple targets having been illuminated with different PRF codes. 
 
     
     
       12. The method of  claim 1 , further comprising
 displaying an angle with respect to null for each of the spots of received laser light. 
 
     
     
       13. The method of  claim 1 , wherein sizes of the spots are increased to be sufficiently large to impinge on multiple quadrants of the detector, and further comprising:
 determining centroids for the spots: and 
 providing outputs representing elevation and azimuth of the centroids of the spots relative to a boresight direction. 
 
     
     
       14. The method of  claim 13 , further comprising:
 providing the outputs representing elevation and azimuth for each of multiple objects being illuminated, each tagged with a code to allow for identification of their respective designators. 
 
     
     
       15. The method of  claim 1 , further comprising:
 calculating azimuth and elevation angular co-ordinates for centroids of the spots by measuring energy of the received laser light in each quadrant of the detector. 
 
     
     
       16. The method of  claim 1 , wherein the quadrant detector comprises two quadrant detectors, and further comprising:
 disposing a first of the two detectors effectively in front of a focal plane; 
 disposing a second of the two detectors effectively behind the focal plane; and 
 combining outputs of the two detectors to reduce inconsistencies of amplitude within the spots. 
 
     
     
       17. Method of locating at least one object being illuminated by a laser designator comprising:
 providing a tracker having a quadrant detector in a field of view; 
 receiving laser light scattered by the at least one object being illuminated; 
 causing the received laser light to impinge as a corresponding at least one spot on the quadrant detector; 
 for each of the spots of received laser light impinging on the detector, determining an angle of the spot of the received laser light relative to a center of the field of view; 
 calculating azimuth and elevation angular co-ordinates for centroids of the spots by measuring energy of the received laser light in each quadrant of the detector; and 
 adding signals from the quadrants on each side of an axis of interest, and deriving a ratio of these quadrants such that that the ratio varies as the spot traverses the quadrants across the axis of interest. 
 
     
     
       18. The method of  claim 17 , further comprising:
 adding signals from the quadrants on opposite sides of an axis of interest, and deriving a ratio of these quadrants such that that the ratio varies as the spot traverses the quadrants across the axis of interest. 
 
     
     
       19. Method of locating multiple objects being illuminated by at least one laser designator comprising:
 providing a tracker having a quadrant detector in a field of view; 
 receiving laser light scattered by the multiple objects being illuminated; 
 causing the received laser light to impinge as corresponding multiple spots on the quadrant detector; 
 for each of the spots of received laser light impinging on the detector, determining an angle of the spot of the received laser light relative to a center of the field of view; and 
 wherein the quadrant detector comprises two quadrant detectors, and further comprising: 
 disposing a first of the two detectors effectively in front of a focal plane; 
 disposing a second of the two detectors effectively behind the focal plane; and 
 combining outputs of the two detectors to reduce inconsistencies of amplitude within the spots.